The arrests occurred after picketers assembled outside the Massachusetts Bay Transportation Authority's so-called "money room" to prevent workers and armored cars from entering the facility in the city's Charlestown section.

Hours later, the MBTA's Fiscal and Management Control Board voted 4-0 to award Virginia-based Brink's a five-year, $18.7 million contract to oversee the money room, a move expected to save the agency about $8 million annually.

Union officials said outsourcing would cost workers their jobs, though MBTA officials said dozens of money room employees would be offered jobs driving buses - which many had done prior to their current positions.

Carmen's Union president James O'Brien and other members of the executive committee were charged with unlawful assembly, union spokeswoman Cayenne Isaksen said, after padlocking a gate outside the building during the pre-dawn protest. The seven pleaded not guilty during court appearances and were released on personal recognizance.

The privatization plan followed an outside review that found widespread security issues at the facility that collects and counts an estimated $119 million in cash annually placed by riders in fare boxes and ticket vending machines. The lapses included security doors that were propped open, allowing unsecured access from outside the building.

"Change is never easy," Brian Shortsleeeve, MBTA acting general manager, said before the control board's vote. "But frankly the status quo at the T just isn't cutting it."

In a letter sent Wednesday to board members, O'Brien criticized the review as a "scorched Earth audit," that included "baseless" claims of MBTA workers cutting sunroofs into money room trucks.

O'Brien argued that privatization was being pushed largely without public scrutiny and that MBTA officials and Republican Gov. Charlie Baker were determined to pursue outsourcing before negotiating an agreement with the union or considering other alternatives.

"We are dealing with a broken system that needs investment, end of story," O'Brien wrote. "We don't need to hand the keys over to a private company seeking to make a profit off of our public tax dollars and riders' fares."

The control board was created last year in the aftermath of a severe winter that crippled the MBTA and exposed widespread managerial and financial weaknesses. The Legislature also gave the transit system a temporary exemption from a state law that sharply limits privatization of government services.

Baker said he supports the union's right to protest unless it interfered with MBTA operations.

"You can't lock the gates or get in the way of the trucks. At some point we have to be able to serve the public," Baker said in defending the decision by transit police to arrest the picketers.

Labor leaders said they expect the Brink's contract to be the first of many privatization deals for the nation's fifth-largest transit system, which has struggled with chronic operating deficits and aging infrastructure. The board recently acknowledged in a report to lawmakers that outsourcing of bus drivers and maintenance operations also is being considered.

A fifth board member, Brian Lang, did not attend Thursday's meeting but told colleagues he would have voted against the contract had he been there. Lang is an official with the city's hotel workers union.